Gas turbosets, such as, for example, stationary gas turbines and also mobile gas turbines, can be optimized with regard to both the efficiency and the output. Modern gas turbosets therefore normally can have very small output reserves stretching beyond the rated output.
In order to increase the output beyond the rated output, water or another suitable liquid can be introduced into the compressor flow of the gas turbine by injection or spraying. The increase in output achieved as a result is accounted for by the fact that the liquid vaporizes after the spraying, as a result of which heat is extracted from the air flowing through the compressor. This vaporizing process taking place continuously constitutes, as it were, continuous intermediate cooling of the compressor flow and this means that, in order to compress the compressor flow to a predetermined level, less compressor work has to be done than would be necessary without the introduction of water. At the same time, the air mass flow rate through the compressor is increased. Thus, at an approximately constant combustion chamber outlet temperature, a higher output can be converted in the turbine of the gas turbine and used, for example, as shaft output.
Such spraying or injection of water for increasing the output of a gas turbine is known, for example, from Patent DE 25 49 790 or also FR 1 563 749.
The spraying or injection of water may be effected upstream of the compressor or else also in one of the compressor stages. For reasons of simplicity and efficiency, pressure atomizer nozzles are often used for spraying the water, in addition to atomizer nozzles assisted by an auxiliary medium, such as air-assisted atomizer nozzles for example. Demineralized water is normally sprayed or injected, which is pumped from a supply tank by means of one or more pumps and fed to the atomizer nozzles. To this end, the pumps deliver a relatively small mass flow of the water to be introduced at a high pressure. Centrifugal pumps are unsuitable for this mode of operation, since, at the operating points required, said centrifugal pumps either cannot be operated at all or can only be operated at a very poor efficiency. Therefore piston pumps are mostly used here. However, piston pumps have to serviced frequently on account of the high mechanical loads acting on them and therefore have only a relatively short service life. The risk of an unforeseen failure of one or more of the piston pumps is also very high. Consequently, modern gas turbines which are designed with water injection frequently have to be shut down or at least operated without output-increasing water injection in order to be able to service or exchange the pumps.